1. Field of the Invention
The present invention relates to a controlling circuit for actuator, and more particularly it relates to a controlling circuit for actuator which rotates a rotor having a permenent magnet by a stator having an electro-magnet so as to change over, for example, an oil-passage area of a hydraulic shock absorber of a damping force adjustable type suspension system.
2. Description of Related Art
As a controlling circuit for actuator, such as an actuator and a controlling circuit for the actuator which adjust the rotational position of a shaft for changing over an oil-passage area in a damping force adjustable hydraulic shock absorber for vehicle are known in Japanese Utility Model Application Laid-Open No. 63-131576(1988) and the like.
The actuator and its controlling circuit disclosed in the Japanese Utility Model Application Laid-Open No. 63-131576 (1988) are "provided with a casing, an output shaft rotatably mounted in said casing, a rotor with a main permanent magnet fixed to a periphery of said output shaft, a stator with a plurality of electro-magnets fixed in spaced apart relation with each other in the circumferential direction thereof in said casing, and exciting circuit forming means for allowing to generate a repulsive magnetic field of the main permanent magnet in at least an electro-magnet which is opposite to the main permanent magnet in the plurality of electro-magnets and for selectively magnetizing a suction magnetic field of the main permanent magnet in an electro-magnet which is in a position ahead of the main permenent magnet to be rotated when said rotor is driven, wherein a sub permanent magnet for generating resiliency in the rotating direction of the rotor is arranged, in both sides of the circumferential direction of said main permanent magnet, between said selectively magnetized electro-magnets whose direction of magnetic fields are set to be opposite to that of the main permanent magnet".
This type of actuator, which is provided with a rotating shaft rotatably mounted in a casing, a rotor having a permanent magnet fixed in a periphery of the rotating shaft, and a stator having a plurality of electro-magnets, rotates the rotating shaft fixed to a change-over shaft of the shock absorber so as to stop it at a desired rotational position by selectively magnetizing the plurality of electro-magnets.
In such a controlling circuit for actuator of prior art as mentioned above, it has been thought that it is necessary to change over a plurality of switches in a complicated manner and that generally it is indispensable to employ an electronic switch to be switched by to a predetermined controlling logic and the controlling logic itself.
As such a controlling circuit for actuator as mentioned above, there is another arrangement that a controlling circuit as mentioned above is constructed with a plurality of mechanical switches only, by which the rotating shaft changed over to a predetermined angle position. In this arrangement, however, the electro-magnets are always to be electrified as long as an ignition swtich is ON, then, there exists a problem that unnecessary heat for the actuator are generated. In order to avoid this generated unnecessary heat for the actuator, it can be thought to provide in the actuator a mechanism for opening/closing said mechanical switches in cooperation with rotation of the actuator, however, effectively it is mechanically difficult to provide such a mechanism and there should occur a problem in durability of mechanical contact point.